My brush is not affect in weight paint mode
Okay so I figured out that for some reason you can now select individual faces to select.
On the top left of this picture there is a face and a vertex option to show their respective geometry. So when you are in that mode you can deselect all faces so that now you cannot have any influence on any faces. All you have to do is deselect everything with either  Alt + A which is the default for 2.8 or press A again to toggle between selected and deselected if you are using the old hotkeys.